Polymeric films such as biaxially oriented polypropylene (BOPP), biaxially oriented polyethylene terephthalate (BOPET), or polyester films have been widely used in variety of applications, for example, in print labels, cartons, labels, shrink sleeves, or flexible packaging materials for food, liquids, and toiletries. Such films are also often printed with the use of high-speed digital printing machines utilizing liquid or dry toners or inks in electrophotographic systems. In such systems, toner images are formed on a photosensitive drum and then electrically transferred onto an intermediate transfer blanket or belt for printing onto a polymeric film sheet or web. Printers using such toners or inks are commercially available from Hewlett-Packard Company under the trade name HP Indigo. However, as liquid toners do not always transfer well and/or adhere well to polymeric film substrates which are printed using such presses, the substrates are typically coated with a primer to enhance the adhesion of liquid toners thereto.
A number of primers have been developed for use on polymeric film substrates which render the surface of the films more receptive to toners and inks. Typical primers currently in use have been developed based on ethylene-acrylic acid copolymers. One such primer is described in commonly-assigned U.S. Pat. No. 7,470,736.
However, the development of newer, high speed digital presses has presented new challenges to the use of primers with regard to liquid toner and/or ink transfer and adhesion to the polymer substrates. For example, the more recently developed HP Indigo 6000 series of digital presses offer digital printing at about twice the speed of previous Indigo presses. In addition, the HP 20000 digital press is capable of printing a 30-inch (76.2 cm) wide film and the HP 30000 digital press is capable of printing at a 29.5 inch (75.0 cm) width on a variety of substrate types.
Due to the specifications of the liquid toners used in such presses, conventional primers do not provide sufficient toner adhesion to the underlying polymeric substrate. As a result, substrates coated with conventional primers may experience undesirable toner transfer to and adhesion to the substrate. Accordingly, there is a continual need for a primer which provides good toner and/or ink adhesion to polymeric substrates.
Additionally, ink adhesion for conventional primers and coated substrates may be impacted when the primer and/or the coated substrate is exposed to water or other chemicals. Consequently, there is also a need for primers which are resistant to damage from water and/or chemicals and thereby also maintain the desired ink adhesion.